Similar experience here but finally succeeded! Here's the summary
Decided to (finally) update MacBook from SL 10.6.8 to Lion (it can't run ML or Mavericks) so this week purchased from UK Apple store. Received redemption code from Apple via email after couple of days and successfully redeemed this in Apps Store.
Under Purchases in Apps Store clicked on "download" and nothing happened! Clicking on the app name "OS X Lion" gave the message "The item you've requested is not currently available in the UK Store". Contacted support but got no useful help there.....
Following day went back to Apps Store and tried again clicking Download - still nothing (apparently - see below) so started thinking upgrade unlikely and £14 wasted.
A little later noticed new icon in Dock and investigating it said downloading Lion - checked Activity Monitor and indeed my internet connection was being hammered. At a little over 4Gb got an error message saying download could not complete (needless to say not happy) and download icon disappeared!!
So with nothing to lose reclicked Download in Apps Store and again no obvious activity and this time no new download icon in Dock - decided to check Activity Monitor again (just in case) and again high level of download activity! Maybe, just maybe, I thought and after about 90 minutes the Lion install screen appeared!
Have now backed up the Installer and successfully installed 10.7.4
I can't offer any explanation why it finally worked - Apps Store still shows "Download" not "Installed" as I would expect and the item is "..still not available.."!